With previous cars that used regular oil, manufacturers recommended oil changes every 7.5K miles. I did them every 5K miles and my engines were always spotless.
In my e90, with synthetic oil, the service indicator suggests oil changes every 15K miles (rural driving). So far, I've been splitting that interval in half and doing them every 7.5K miles.
When I did my last oil change, my SA recommended NOT doing additional oil changes, even if I plan on keeping my car a long time, and that was based on examining engines that had well over 100K miles on them. I understand the school of thought that says that BMW recommends long service intervals because it keeps their free maintenance costs down, but it is also in BMW's interest to have satisfied customers with engines that last a long time. Plus, every time we have someone touch our cars, we risk someone making a mistake (overfill, underfill, leaks, improperly torqued bolts, etc.). So I've concluded the following:
- For normal driving, the recommended oil change interval is probably fine.
- For normal driving, enthusiasts that want a margin of safety should probably change their oil every 10K miles.
- For hard driving, enthusiasts should probably change it every 7.5K miles.